This invention in general relates to electronic printing and in particular to an electronic printing process in which high-contrast film is used to make copies of original pictorials.
Electronic printing is well-known and refers to a method in which a flying spot scanner, instead of a continuous light source, is used to photographically make copies of original pictorial materials.
In the usual photographic copying process used to make enlargements or contact prints, a continuous, more or less uniform source evenly illuminates all parts of the negative simultaneously for some appropriate exposure interval arrived at either through trial and error but more likely by automated means.
In electronic printing, the flying spot (typically an electron beam moving over the surface of a cathode ray tube) is the light source. Here, the image is formed by exposure of one spot of the negative at a time like the image in a television screen is formed. During the exposure, the scanning beam moves over the whole negative area in a raster pattern that assures that the spot passes over every point in the negative for the same length of time.
In electronic printing systems, the intensity of the electron beam is controlled according to the density of the negative area that the beam is passing over at any instant. To accomplish this, the light coming through the negative is monitored by a photodetection system whose output is fed back into the circuit controlling the scanning spot intensity. With no feedback, the spot remains uniformly bright all the time as with a continuous light source. With 100% negative feedback, the spot intensity automatically compensates for variations in negative density, and the resulting print is uniformly gray. With excessive positive feedback, contrast between light and dark areas can be exaggerated, at the expense of a realistic tonal range. Between these two extremes of feedback, there are intermediate degrees which produce prints of lower or higher contrast so that negatives of varying degrees of contrast can be printed on a single grade of paper, usually of low contrast. Moreover, this system of contrast control reduces the overall tone range of the negative image without reducing the fine detail contrast to the same extent. However, the detail reproduction is limited, of course, by the size of the flying spot which, if large, reduces detail and, if smaller, enhances detail.
Hence, prints produced in an electronic enlarger reproduce all of the fine detail, even of very contrasty negatives without exceeding the contrast range of the paper. The effect of the flying spot scanner exposure is that of an unsharp, contrast reducing mask which is virtually a luminance positive low contrast image of the negative being printed and produced during the printing exposure.
The principle underlying electronic printing can be used for producing either black and white photographs or color photographs from color negatives. Color negatives are printed by three successive exposures through a red, green and blue tricolor filter. During each exposure, the photodetector reads through a complementary colored filter to provide the necessary feedback control.
Scanning light sources need not be confined to just the electron beam of a cathode ray tube. Laser scanning and printing apparatus are also well known for electronic printing. One example, which utilizes a laser to simultaneously provide a first laser beam for scanning an original pattern to derive pattern signals corresponding to the tones on the original pattern, and a second laser beam for projecting recording light onto a recording medium, is disclosed in U.S. Pat. No. 3,622,690 entitled "Electronic Scanner Utilizing a Laser for the Simulaneous Scanning and Reproducing of Images" by A. Stephens et al, issued Nov. 23, 1971. This patent also discloses a color correction computer to correct for deficiencies in the printing dyes. Thus, pictorial materials are scanned in laser light and converted to elecronic signal information by photoresponsive devices which detect the scanning beam. The electronic signal information is then modified by appropriate algorithms to provide an enhanced image on the printing of the reproduction. During the printing process, the laser light, modulated in accordance with the enhanced signal information, is line scanned aross the surface of the reproduction material to directly expose a duplicate image of the oiriginal pattern. Since the laser light is utilized to directly scan and expose the photosensitive material for the reproduction, the original pictorial material must be line scanned and sensed in high resolution in order to provide a high resolution duplicate. Consequently, the resolution of the duplicate image is no greater than the resolution at which the original pictorial materials are scanned.
Line scanning an original pattern or picture in high resolution to provide image data for minute picture elements or pixels results in the generation of an enormous amount of data needed to define the image in such fine detail. When converted to digital format, this data occupies a considerable amount of memory storage and requires considerable processing capability when electronic image enhancements, such as color correction, are incorporated into the system to provide high quality electronic images. Consequently, one is faced with either the prospect of a very large, fast computer or a smaller, slower clock computer that requires longer image processing, and thus, copy time.
Another possibility, described in the parent of this application, Ser. No. 730,828, filed May 6, 1985, involves a low resolution scanning system along with an optical imaging system, both of which operate in conjunction with one another to reduce the image data requirements while at the same time providing the possibility for high resolution copies. The strategy of the system described in that application was to divide the illumination and imaging tasks between two separate components of the system. However, to fully exploit this strategy, it has been discovered that use must be made of high-contrast copy materials as described in the detailed disclosure which follows.
Therefore, it is a primary object of this invention to provide a method in which an electronic scanning and printing apparatus is used in conjunction with high-contrast film to provide sharpness enhanced image duplicates of an original picture that is scanned in low resolution to provide only a minimal quantity of image illumination data.
It is a further object of this invention to provide a method in which a laser scanning and printing apparatus is used to make sharpness enhanced duplicates of an original by scanning the original in low resolution.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the method possessing the combination of steps which are exemplified in the following detailed disclosure.